Faceted Bone Screw Thread Design for Torque Reduction
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Solution Overview
Problem
Orthopedic screws face issues such as bone splitting during insertion due to high torque requirements and potential loosening post-installation, which can lead to mis-setting of bones and require additional procedures for correction.
Innovation Solution
The development of a faceted bone screw with varying thread depths and angles, manufactured using a Swiss type screw machine, which reduces friction and enhances osteointegration by creating peaks and valleys, thereby reducing the torque required for insertion and preventing loosening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional smooth-threaded bone screws are used, then the insertion process is simple, but high torque is required which causes bone splitting
Solution Approach 1:
The screw thread is designed with varying local qualities through facets at different angles (alpha and beta facets) and varying thread depths. This creates regions of different friction characteristics along the thread, allowing some portions to engage bone while others reduce friction, thereby reducing overall insertion torque and preventing bone splitting.
Solution Approach 2:
The continuous thread surface is segmented into multiple facets (alpha facets and beta facets) with different orientations. This segmentation creates discrete contact regions that distribute the insertion force more evenly, reducing peak stresses that would otherwise cause bone splitting.
2Reliability
If conventional smooth-threaded bone screws are used, then the installation procedure is simple, but the screws may loosen or back out after installation
Solution Approach 1:
The screw thread employs asymmetric facet arrangements with different alpha and beta angles, creating an asymmetric friction profile. This asymmetry provides higher resistance to loosening forces while maintaining acceptable insertion characteristics, improving screw stability without requiring complex additional features.
Solution Approach 2:
Instead of making the entire thread surface smooth for easy insertion (conventional approach), the invention inverts the approach by creating a faceted surface that appears more complex but actually reduces insertion torque through strategic friction reduction zones, while simultaneously improving anti-loosening properties.
3Reliability
If faceted threads with varying depths are created, then osteointegration is enhanced, but the manufacturing process becomes more complex
Solution Approach 1:
The manufacturing process uses periodic cutting actions with the forming tool, alternating between cutting alpha facets and beta facets in a repeating cycle. This periodic manufacturing approach simplifies the overall process compared to creating completely variable thread geometries, while still achieving the desired faceted structure for enhanced osteointegration.
Solution Approach 2:
The invention employs controlled parameter changes in the thread geometry, specifically varying the depth and angles of facets in a systematic pattern rather than creating completely irregular geometries. This allows for enhanced osteointegration while maintaining manufacturability through predictable, repeatable manufacturing processes.
Data Source
AI summary
A bone screw and a method for manufacturing the same includes a screw thread configuration having one or more grooves cut into a leading face of the thread, a trailing face of the thread, and/or the shaft between the threads. Other implementations include the incorporation of facets into the one or more grooves. The implementation of the one or more grooves increases the surface are of the orthopedic screw and functions to increase in anchoring the bone screw within the bone once inserted therein, and thereby reduce the possibility for the screw backing out after insertion.